Bug 477815

Created attachment 163685 [details]
System information generated by the Krita help menu

SUMMARY  
***
Sometimes rectangular glitches will appear on the canvas when I'm painting with a textured brush with a size approaching half of the canvas. The glitch can be seen in the screenshot that will be attached next.
***

STEPS TO REPRODUCE  
1. (On Microsoft Windows) set the canvas renderer to "DIRECT3D 11 VIA ANGLE".
2. Select one of the default textured brushes (Krita 4 Preset Bundle).
3. Paint a continuous stroke on the canvas, until the glitch appears. It's rare for it to appear.

OBSERVED RESULT  
If I rotate, pan or zoom the canvas then the glitch is rotated/panned/zoomed together, as if it was part of the painted pixels.  
If I undo and then redo, the glitch disappears and the painted pixels that were underneath it can now be seen, and there are no defects to what was painted.  
If I set the canvas renderer to OpenGL, these glitches stop happening altogether. On my system this renderer works fine, so I'll be using this instead of the default renderer.

EXPECTED RESULT  
For no glitch to appear.

SOFTWARE/OS VERSIONS  
(Please see the attached system report from the Help menu for more details)
  Build ABI: x86_64-little_endian-llp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: winnt
  Kernel Version: 6.3.9600
  Pretty Productname: Windows 8.1 Version 6.3 (Build 9600)
  Product Type: windows
  Product Version: 8.1

ADDITIONAL INFORMATION
----